<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        div{
            width: 100px;
            height: 100px;
        }
        .b1{
            background-color: red;
            float: left;
        }
        .b2{
            background-color: green;
            height: 200px;
           
        }
    </style>
</head>
<body>
    <div class="b1"></div>
    <div class="b2"></div>
</body>
</html>